FIG. 3 shows the prior art structure of an expansion valve placed inside a refrigeration cycle of an air conditioner on a vehicle. The expansion valve comprises a high-pressure refrigerant path 2 where the liquid refrigerant to be decompressed enters and a low-pressure refrigerant path 3 where the gas-phase refrigerant exist. The valve further has a valve hole 4 comprising a throttle hole with a small radius positioned on the high-pressure refrigerant path 2. Therefore, the liquid refrigerant flowing into the high-pressure refrigerant path 2 from a receiver tank 32 will experience adiabatic expansion by passing the valve hole 4 having a small flow area.
The open-hole portion of the refrigerant flow-in side of said valve orifice 4 is a valve seat. In this valve seat portion a ball-shaped valve means 5 is positioned to change the opening area of the valve orifice 4. The valve means 5 is supported by a ball receiver 7, and a compression coil spring 9 positioned between the ball receiver 7 and an adjusting nut 8 adds force to the valve means 5 toward the closing direction of the valve (pressing the valve means 5 into the valve seat portion of the valve orifice 4).
Reference 10 is a pressure housing positioned on the upper end of the valve body 1 for sensing the temperature of the gas-phase refrigerant and comprises a diaphragm 11 for driving the valve means 5 via an operation shaft 6, a sealed chamber 12 for holding the heat sensing gas partitioned by said diaphragm, and a pressure-equalizing chamber connecting to the low-pressure refrigerant path 3.
A hole 15 is placed on the outer wall 14 of said housing 10. When the heat sensing gas is filled from this hole into the sealed chamber, a metallic plug body 16 is utilized to seal the hole 15 on the outer wall, maintaining the pressure of the filled sensing gas.
Therefore, the sealed chamber 12 senses the temperature of the gas-phase refrigerant flowing through the low-pressure refrigerant path 3, and following the temperature change of the gas-phase refrigerant the pressure inside the sealed chamber 12 changes. On the other hand, the pressure-equalizing chamber 13 positioned on the lower stream of the diaphragm 11 is connected to the low-pressure refrigerant path 3 and has an equivalent pressure as the gas-phase refrigerant flowing through the low-pressure refrigerant path 3, so that the diaphragm 11 is displaced by the difference between the pressure inside the sealed chamber 12 and the pressure inside the pressure-equivalizing chamber 13. The displacement is transmitted via the operation shaft 6 to the valve means 5 and the opening of the valve orifice 4 is controlled.
The prior art expansion valves have the hole peripheral area of the housing outer wall 14 and the plug body 16 contacting each other by a tapered surface and welded together by an electrical resistance weld, for example, a projection weld. A concave portion is formed around this projection weld portion. To prevent water from gathering inside the concave portion, a projection 16a of the plug body 16 is inserted to the hole 15 on the outer wall of the housing, and the conical portion 16b of the plug body 16 is welded by a projection weld to form a projection weld portion 17, and the plug body 16 is welded to the outer wall 14 of the housing as is shown in FIG. 4. Then, a corrosion inhibitor 21 of an adhesive and the like is filled on the outer area. The expansion valve having such structure is shown in Japanese Patent Application Laid-Open No. H8-226567.
In these kinds of prior art expansion valves, the plug body 16 was welded only by projection weld on to the hole 15 on the outer wall of the housing, so the weld strength by the projection weld must be improved in order to perform the seal securely.
The present invention provides a heat expansion valve that improves the above-mentioned structure and enables a secure seal of the plug body to the hole on the outer wall of the housing by projection welding only, and at the same time prevents the corrosion of the peripheral of the projection weld on the outer w all of the housing.